package demo1;

/**
 * @Author liangzai
 * @Description:
 */
public class Test {
    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<>();
        for(int i = 0;i < s.length();i++) {
            char ch = s.charAt(i);
            if(ch == '(' || ch == '{' || ch == '[') {
                stack.push(ch);
            }else {
                if(stack.isEmpty()) {
                    return false;
                }
                //此时开始判断是否匹配
                char ch2 = stack.peek();
                if(ch == ')' && ch2 == '('
                        || ch == '}' && ch2 == '{'
                        || ch == ']' && ch2 == '[') {
                    stack.pop();
                }else {
                    return false;
                }
            }
        }
        if(!stack.isEmpty()) {
            return false;
        }
        return true;
    }
    public int evalRPN(String[] tokens) {
        Stack<Integer> stack = new Stack<>();
        for(String str : tokens) {
            if(!isOperator(str)) {
                int x = Integer.parseInt(str);
                stack.push(x);
            }else {
                int val2 = stack.pop();
                int val1 = stack.pop();
                switch(str) {
                    case "+" :
                        stack.push(val1+val2);
                        break;
                    case "-" :
                        stack.push(val1-val2);
                        break;
                    case "*" :
                        stack.push(val1*val2);
                        break;
                    case "/" :
                        stack.push(val1/val2);
                        break;
                }
            }
        }
        return stack.pop();
    }

    public boolean IsPopOrder (int[] pushV, int[] popV) {
        // write code here
        Stack<Integer> stack = new Stack<>();
        int j = 0;
        for(int i = 0; i< pushV.length;i++) {
            stack.push(pushV[i]);
            while(!stack.empty() && j < popV.length &&
                    stack.peek() == popV[j]) {
                stack.pop();
                j++;
            }
        }

        return stack.empty();
    }
}
